Electrical testing of semiconductor die has become an integral part of the semiconductor manufacturing process. Semiconductor die may be tested during various stages of manufacturing, for instance prior to plastic assembly, and just prior to shipment to customers. One goal of this testing is to identify defective parts before they are shipped to customers. However, falsely identifying good parts as defective parts can be very costly for the semiconductor manufacturer. Consequently, the reliability and accuracy of the equipment associated with the testing process is very important.
For electrical testing, the semiconductor packages are typically loaded into a test socket by a handler. The test socket and handler align the package so that electrical contacts on the package can be connected to a test board using electrical conductors such as pogo pins. The pogo pins are maintained in fixed positions in the plane of the test socket, but are capable of compressing perpendicular to the plane of the test socket to allow good contact with the electrical contacts of the semiconductor package. However, since the pogo pins can't move horizontally, the alignment of the semiconductor package with the pogo pins is critical. Conventional test sockets have a central cutout into which the semiconductor package fits. This cutout aligns the package along its edges, but can allow for some misalignment when the package dimensions are slightly smaller than expected. This misalignment can lead to bad contact (open connections) between the pogo pins and the electrical contacts on the package. A test socket that aligns the package using the corners of the package would therefore provide for more precise alignment and prevent open connections due to package misalignment.
In recent years, advancements in circuit design and semiconductor manufacturing have drastically reduced the size of semiconductor packages. As an example, chip-scale packages are commonly manufactured where the size of the overall package is approximately the same size as the semiconductor die. The decreasing size of the semiconductor packages means that the electrical contacts of the smaller packages are spaced closer together and in some cases are smaller. This presents challenges for the testing process because the testing equipment must be able to reliably contact all of the electrical contacts of the semiconductor package.
The semiconductor packages are typically manufactured in groups (either in wafer form or on substrate strips) and then singulated. As the packages become smaller, slight variations in the singulation process can lead to significant differences in final package dimensions. These slight variations in the singulation process may be caused by the type of singulation blade used, the amount of wear the blade has, and alignment tolerances of the singulation equipment. The variation in package dimensions can lead to misalignment in the test socket, as described above.
When combined together, the small package size, the tightly-packed electrical contacts, and the package dimension variation can lead to significant problems in the testing process. These problems can lead to good packages being falsely identified as failing the electrical tests, which can cause significant losses to the semiconductor manufacturer. Consequently, a test socket that is capable of precisely aligning small semiconductor packages, despite variations in package dimensions, is desired.
The invention addresses these and other disadvantages of the conventional art.